1. Field of the Invention
The invention relates to a system that uses a wireless microphone to transfer audio to an image pickup apparatus, a recording apparatus, or an audio mixer, and also relates to a wireless microphone, an audio transmitting apparatus, an audio receiving apparatus, an image pickup apparatus, a recording apparatus, and an audio mixer that construct such a system.
2. Description of the Related Art
In recent years, in the field of television broadcasting, it has become common to transfer audio using wireless microphones. FIGS. 1A and 1B show two examples of the appearance of a wireless microphone. Of such drawings, where FIG. 1A shows wireless microphone transmitters (hereinafter simply called “transmitters”) as apparatuses for transmitting audio. Each of the transmitters 81, 82 fundamentally includes a microphone (in the case of the transmitter 82, a pin microphone, not shown, that is connected by a cable) and a modulating/transmitting unit that transmits radio waves that have been modulated using an audio signal from the microphone. The transmitter 81 is a hand microphone-type transmitter that is held by hand. Conversely, the transmitter 82 is a device that is attached to a waist belt or the like.
FIG. 1B shows wireless microphone receivers (hereinafter simply called “receivers”) as apparatuses for receiving audio. The receivers 83, 84 each fundamentally include a receiving/demodulating unit that receives radio waves transmitted from the transmitter 81 or transmitter 82 and demodulates the audio signal, and an output terminal that outputs the demodulated audio signal to the outside. The receiver 83 is a portable receiver. The receiver 84 is a non-portable receiver and is capable of receiving radio waves from a plurality of transmitters (for example, four transmitters).
FIGS. 2A and 2B are diagrams showing examples of audio transfer systems that use the transmitter 81 and the receiver 83 shown in FIGS. 1A and 1B to record audio during ENG (Electronic News Gathering). In the example in FIG. 2A, the transmitter 81 is used by an announcer conducting an interview. The receiver 83 is attached to a slot provided on a camcorder 91 (i.e., a video camera integrated with a recorder such as a VTR or optical disk apparatus) or is connected to the camcorder 91 by a cable. The audio signal inputted from the receiver 83 into the camcorder 91 is recorded by the camcorder 91 together with the images shot by a cameraman (not shown) using the camcorder 91.
In the example in FIG. 2B, the transmitter 81 is used by an announcer and the receiver 83 is connected by a cable to an audio mixer 92. The audio signal inputted into the audio mixer 92 from the receiver 83 is mixed or switched by an audio man (not shown) using the audio mixer 92. The audio signal outputted from the audio mixer 92 is recorded by a VTR (or audio recorder or camcorder), not shown.
FIG. 3 shows an example of a system that uses a plurality of the transmitters 81, 82 and receivers 84 shown in FIG. 1 to transfer audio signals on multiple channels in a studio. The transmitters 81, 82 are used by the cast (not shown) or the like of a program. Radio waves transmitted from the transmitters 81, 82 are received by antennas 91 that are shared by the receivers 84. The audio signals on multiple channels outputted from the receivers 84 are sent to the audio mixer 92. Data on the audio signal levels and frequencies received by the respective receivers 84 are sent via a hub 93 to a personal computer 94. The frequency, audio signal level, and the like of the audio signal on each channel are displayed on the display of the personal computer 94.
However, when recording audio using such wireless microphones, if a large sound that exceeds the level that was expected when setting the input level of the transmitter (i.e., when setting the attenuation level of an attenuator) is inputted into the transmitter due to a large noise (such as the noise of a car) being unexpectedly produced in the periphery of the speaker, distortion of the audio signal occurs inside the transmitter.
An existing wireless microphone is constructed so that this type of audio distortion is detected inside the transmitter and displayed on a display unit (such as light-emitting diodes or a liquid crystal display) of the transmitter itself, so that the user can check for audio distortion by looking at the display unit.
Other existing methods include connecting headphones or speakers to the audio output terminal of the receiver and actually listening to the audio to check for audio distortion and looking at audio level meters on an audio mixer to check for audio distortion.
However, since a transmitter is small, the display area of the display unit is very small. When ENG (Electronic News Gathering) is carried out as shown in FIGS. 2A and 2B, in many cases the display unit is hidden by the announcer's hand or clothes, and therefore will not be visible to the announcer. Also, for a system inside a studio such as that shown in FIG. 3, there are many cases where the transmitters and receivers are set up some distance away from each other, and it is generally difficult to see the display units of the transmitters from the positions of the receivers.
On the other hand, with the method where the user checks for audio distortion by actually listening to the audio, in addition to needing equipment such as headphones or speakers, special knowledge and experience are also required, with the reliance on human judgments also leading to inconsistencies in such judgments. When such equipment may not be provided and/or when the operator has insufficient knowledge or experience, the filmed material may not be used in some cases.
Also, with the method where audio distortion is checked by looking at audio level meters of an audio mixer, if the levels of the input audio signals inputted into the audio mixer are adjusted using auto-gain controls and/or variable volume controls (faders), the input audio levels of the transmitters themselves will not be displayed on the audio level meters, and therefore it may be to check for audio distortion at the transmitters. Accordingly, it may be necessary to change the settings of the audio mixer so that the input audio levels of the transmitters are displayed. Such settings will require knowledge and experience and are also troublesome.
In particular, when multiple transmitters are used to provide multiple channels as in the example shown in FIG. 3, it will need long time to specify the transmitter at which audio distortion has occurred.
For systems that use a wireless microphone, Japanese Unexamined Patent Application Publication No. 2007-36735 discloses a technology where the receiver detects frequencies unused by radio waves based on the reception level for radio waves and outputs information showing the detected unused frequencies from a communication connector (such information is inputted into a video camera or audio mixer into which the receiver inputs an audio signal and is displayed on a display unit). Consequently, the operator of the video camera or audio mixer can check the unused frequencies and set the frequencies to be used by the wireless microphone system.